Definition: Hypothyroidism, or underactive thyroid, is a condition where the thyroid gland fails to produce sufficient thyroid hormones (T3 and T4) to meet the body’s metabolic needs.
Epidemiology: Hypothyroidism affects approximately 5% of the population globally, with higher prevalence in women and older adults.
Significance: Untreated hypothyroidism can lead to severe complications like myxoedema coma and long-term cardiovascular disease.
2. Causes and Risk Factors
Causes:
Primary Hypothyroidism (most common):
Hashimoto’s thyroiditis (autoimmune destruction of the thyroid gland).
Iodine deficiency or excess.
Thyroid surgery or radioiodine therapy.
Secondary Hypothyroidism:
Pituitary or hypothalamic dysfunction, leading to inadequate TSH or TRH production.
Risk Factors:
Female sex, age >50 years.
Family history of thyroid disorders or autoimmune diseases.
Previous radiation exposure or neck surgery.
3. Pathophysiology
Insufficient thyroid hormone production disrupts metabolic homeostasis. The pituitary gland compensates by increasing TSH secretion in primary hypothyroidism. Reduced thyroid hormone levels lead to slowed metabolic processes, causing characteristic symptoms like fatigue, weight gain, and cold intolerance.
4. Symptoms and Features
General Symptoms:
Fatigue, weight gain, and cold intolerance.
Dry skin, hair thinning, and brittle nails.
Constipation and hoarseness.
Specific Features:
Puffy face, periorbital swelling.
Slow heart rate (bradycardia).
Depression or cognitive impairment (“brain fog”).
Menstrual irregularities (e.g., heavy or irregular periods).
5. Complications
Myxoedema coma: A life-threatening complication characterised by hypothermia, bradycardia, and altered mental status.
Cardiovascular disease: Increased risk due to hyperlipidaemia.
Infertility or pregnancy complications (e.g., miscarriage, preeclampsia).
Goitre: Thyroid gland enlargement due to chronic TSH stimulation.
6. Diagnosis
Clinical Features: Symptoms like fatigue, weight gain, and cold intolerance raise suspicion.
Laboratory Tests:
TSH: Elevated in primary hypothyroidism (>4.0 mIU/L).
Free T4: Low levels confirm hypothyroidism.
Thyroid antibodies (anti-TPO, anti-thyroglobulin): Positive in autoimmune thyroiditis.
Imaging: Thyroid ultrasound or radioactive iodine uptake scan for structural or functional abnormalities.
7. Management Overview
Goals: Normalise thyroid hormone levels, alleviate symptoms, and prevent complications.